The SMTP 538 error often indicates there’s a server issue related to authentication when sending emails from your site.
This error may occur if the recipient’s email client requires a secure connection and the SMTP server is not properly configured to use it.
In some cases, it can occur due to a mismatch in the security protocols between the SMTP server and the recipient’s email client.
Resolving the Error – Solution
To fix this error, check your SMTP server’s security settings to confirm if it’s properly configured. Ensure your server uses the correct encryption method (SSL/TLS) required by the email client.
It’ll also help to review the security settings and ensure they match the recipient’s email client. If you’re not sure how to locate these options, we suggest contacting your SMTP service provider for additional help.